David Cameron is prepared to sanction further changes to the health bill after Downing Street said that ministers were prepared to listen to concerns raised in the House of Lords.

As the health secretary, Andrew Lansley, draws up plans to accept some amendments to the health and social care bill, No 10 said that ministers would not accept significant changes. The use of the word significant confirmed that Lansley would accept some changes if they did not "emasculate" the contentious third section of the bill that deals with competition.

The prime minister's spokesman said: "The health and social care bill is going to be considered by the House of Lords on a number of days over the next couple of weeks and I am not going to pre-empt discussions in the House of Lords.

"We have made clear that we don't see any need for further significant changes to the bill. We had a listening exercise. We made significant changes to the bill. We think that the bill is the right one and the reforms are the right reforms."

The Guardian understands that Lansley will not accept any amendments, due to be tabled by the Liberal Democrat peer Lord Clement-Jones, or sanction any fresh government amendments. He feels two of the Lib Dems' concerns have already been dealt with – the call for foundation trusts to co-operate rather than compete and for trusts to be placed under a duty to achieve greater equality of outcomes.

A third Lib Dem demand, that EU competition law should not apply to the NHS, is more problematic. Department of Health lawyers have advised that the NHS has been covered by this since the Blair reforms. Lansley does not see this as a political problem, but he believes the legal advice makes it difficult to move on this area.

The health secretary is, however, prepared to give ground in two areas later this week. These are that:

• Monitor, the NHS trusts regulator which is charged with improving efficiency, would retain its role in overseeing free-standing trusts beyond 2014.

• The Competition Commission would not have the main role in reviewing the development of competition. This would rest with Monitor.

Simon Hughes, the Lib Dem deputy leader, told the Sunday Politics Show on BBC1: "Watch this space. You will see a bill that will protect and defend the NHS, which was a Liberal idea in the first place."

Clement-Jones is tabling his amendments with the blessing of the party leader, Nick Clegg, in the hope it will defuse a full-scale rebellion at the Lib Dem spring conference next month. Clegg's tacit backing has prompted concerns among some senior Tories that the deputy prime minister is planning to abandon a deal with Cameron to ensure the bill is passed.

The Labour leader, Ed Miliband, increased the pressure on Lib Dem peers on Monday following a warning by Lord Crisp, a former NHS chief executive who helped drive through reforms under Tony Blair, that the government's controversial health reforms are a mess and unnecessary.

Miliband used a column in the Times to invite all those who believe in a comprehensive NHS to join Labour in getting the legislative plans ditched altogether.

"People interested in the NHS to help patients should not – must not – support this bill," he wrote, adding that the bill was not fit for the purpose of meeting the huge challenges faced by the health service.

The legislation would lead to fragmented services, a postcode lottery and the risk of longer waits, he warned.

"Mr Cameron replies that these are necessary reforms. But throwing all the pieces of our NHS up in the air and seeing where they land is not the right way to go about reform," Miliband wrote. "Only political pride is preventing this prime minister from dropping his bill.

"If he ploughs on, he will not only destroy trust in himself, he will also prevent the real change that the NHS needs."

The chancellor, George Osborne, said at the weekend it was essential that the changes went through if the NHS was to be affordable while meeting the needs of an ageing population.

But the reforms were panned by Crisp in one of the strongest attacks on the bill by a former NHS grandee.

The crossbench peer, who served as the chief executive of the NHS between 2000 and 2006, told Radio 4's The World this Weekend: "I think it's a mess. I think it's unnecessary in many ways, and I think it misses the point. I think it's confused and confusing, and I think it's unfortunately setting the NHS back."